bfarnam
commented
2 years ago The Open (Missing) valve detection circuit uses a method of detecting missing valves by providing a small current at approximately +V minus 3 volts in order to measure the current through the valve. There are two separate problems that are causing this issue.
CAUSE
- The three valves share a single open load detection voltage line which causes voltage feedback amongst the three valves.
- The total series resistance of the valves and all wiring harness and connection points needs to be known in order to determine the total expected current. This can be approximated, but could cause an open valve condition under certain circumstances.
RESOLUTION
- The current beta hardware does not provide a blocking diode to isolate the three valves in the open valve detection circuit. The next release of hardware will have the diodes to isolate the valves during open valve detection to stop the feedback between the valve loops.
- Since the total series resistance is unknown, the open valve detection circuit algorithms will need to be modified with a worst case scenarios:
- Minimum and maximum series resistance of the circuit
- Minimum and maximum wiring distance allowed for proper operation
- The maximum number of allowed connections
- The allowed connection types
- The maximum number of valves per zone
The code changes along with above minimums and maximums will be released at a later date yet to be determined.
When the ACU system does not have any valves, or only one valve, the open valve detection does not always work.